Isn't China still on Amazon's list of blocked countries Kindle-wise, at least as far as 3G reception and being able to obtain books goes? Or maybe the Great Firewall is interfering with the downloads.
In any case, if she receives the books via 3G,
there's a 99 cent charge per megabyte outside the US that's paid by the recipient, as detailed in Amazon's Kindle FAQ.
To avoid accidentally incurring the charges, she can go into her Manage Your Kindle page at Amazon and set the max document charges accepted to $0.00, which will effectively block any 3G transfers.